package solution2;
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 *
 * Time complexity : O(max(m, n)). Assume that m and n represents the length of l1 and l2 respectively,
 * the algorithm above iterates at most max(m, n) times.
 * Space complexity : O(max(m, n)). The length of the new list is at most max(m,n)+1.
 *
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode HummyHead = new ListNode(0);
        ListNode current = HummyHead;

        int carry = 0;
        while (l1 != null || l2 != null) {
            int x = (l1 != null) ? l1.val : 0;
            int y = (l2 != null) ? l2.val : 0;
            int sum = x + y + carry;
            carry = sum / 10;
            current.next = new ListNode(sum % 10);
            current = current.next;
            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;
        }

        if (carry > 0)
            current.next = new ListNode(carry);
        return HummyHead.next;
    }
}